Multi-stage compressor section number optimization method based on impeller passage Mach number
By introducing the impeller flow channel Mach number optimization into the design of multi-stage compressors, the problems of high design difficulty and gas temperature rise under high pressure ratio are solved, achieving a reduction in the number of stages, lower cost, and improved performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-18
- Publication Date
- 2026-03-31
AI Technical Summary
Existing technologies make it difficult to find the optimal solution when designing multi-stage centrifugal compressors, which increases the difficulty of design and manufacturing. Furthermore, the gas temperature rises significantly under high pressure ratios, increasing the danger of the medium and the design difficulty.
By introducing the impeller flow channel Mach number as a reference parameter, the number of stages in a multi-stage compressor is optimized. CFD software is used to calculate the flow channel Mach number distribution, and the impeller speed, outer diameter, and inlet cover diameter are adjusted to reduce the number of stages and improve efficiency.
This achieves the reduction of compressor stages without compromising efficiency, thereby lowering production costs and structural complexity, and improving overall machine performance and operational stability.
Smart Images
Figure CN121765863A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of centrifugal compressor optimization design technology, and relates to a method for optimizing the number of stages in a multi-stage compressor based on the Mach number of the impeller flow channel. Background Technology
[0002] Centrifugal compressors are an important branch of compressors. Benefiting from their high flow rate, high pressure ratio, and high efficiency, they are widely used in national economic sectors such as chemical engineering and aerospace, and are important domestic and export products in my country's industrialization process. However, in the international market, the design and manufacturing processes of Chinese compressor products have not reached first-tier levels, making it difficult to establish a firm foothold in the high-end market. Therefore, continuing to steadily improve the design and manufacturing levels of centrifugal compressors, and enhancing product performance and operational stability, is the inevitable path to ultimately improve the quality of Chinese compressor products and expand their market share both domestically and internationally.
[0003] In some compressor applications, when the compressor pressure ratio is very high, the required variable compression work becomes very large, or excessive demands are placed on parameters such as impeller strength, bearing load, coaxiality, and runout, making design and manufacturing difficult. The common solution in this case is to use multi-stage impellers to perform work on the gas, i.e., using a multi-stage centrifugal compressor. However, due to the high pressure ratio requirements, the gas temperature rises significantly, resulting in more compression work required to achieve the same pressure ratio, and also increasing the danger of some special media. Therefore, adding intercoolers between some stages can achieve energy savings by reducing the compression work required by the next stage without changing the pressure ratio distribution. The stages separated by the intercoolers are called sections.
[0004] The introduction of stages and sections greatly expands the application scenarios of compressors, significantly improving their versatility. However, the specific selection of the number of stages and sections also significantly increases the design difficulty. Generally, to ensure good compressor performance, several different stage and section schemes are initially selected based on the principle of minimum power saving or experience. After designing each scheme separately, the optimal scheme is determined through comparison. This traditional design approach not only increases the workload of designing, calculating, and verifying multiple initial schemes but also limits the ability to find the optimal solution due to the limitations of the initial scheme's design level.
[0005] To address this issue, a method for optimizing the number of stages in a multi-stage compressor based on the Mach number of the impeller flow channel is designed to overcome the aforementioned problems. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for optimizing the number of stages in a multi-stage compressor based on the Mach number of the impeller channel. Based on existing technologies, this invention provides and supplements a method for optimizing and designing the number of stages in a multi-stage compressor after determining the number of stages based on the principle of minimum power saving. In the initial design process, by introducing the impeller inlet Mach number as the main reference parameter, a reliable method for optimizing and designing the number of stages in a multi-stage compressor is proposed.
[0007] This invention is achieved through the following technical solution: a method for optimizing the number of stages in a multi-stage compressor based on the Mach number of the impeller channel. After determining the number of stages based on the principle of minimum power saving, the method further optimizes and designs the number of stages of the multi-stage compressor based on the Mach number of the impeller channel. In the process of adhering to the principle of minimum power saving, the impeller inlet Mach number is introduced as the main reference parameter, and a reliable method for optimizing and designing the number of stages of the multi-stage compressor is proposed. The method includes the following steps: 1) Calculate the Mach number of the impeller flow channel: The Mach number distribution in the meridional flow channel and the blade-to-blade flow channel can be obtained by using the Mach number calculation module in various CFD software. 2) Based on the Mach number of the impeller flow channel, increase the impeller speed, impeller outer diameter, and inlet cover diameter in the later section; 3) Apply impeller design based on the Mach number of the impeller flow channel with the goal of reducing the number of stages.
[0008] Preferably, the specific method for increasing the impeller speed, impeller outer diameter, and inlet cover diameter in step 2) is as follows: 1) Increasing impeller speed: can significantly improve the impeller's work capacity. With the mass flow rate remaining constant, the impeller does more work on the gas medium, resulting in a greater increase in the gas pressure head and velocity head, ultimately leading to a higher pressure ratio; 2) Increase impeller outer diameter: Increasing the impeller outer diameter also means increasing the blade length, which in turn increases the work done by the impeller. When increasing the impeller outer diameter, the blade profile and placement angle should also be adjusted to obtain the maximum impeller efficiency. 3) Increase the diameter of the inlet cover: Increasing the diameter of the inlet cover will increase the inlet cross-sectional area, further reducing the loss of the medium at the impeller inlet. At the same time, it will increase the load at the turn of the impeller, slightly increasing the impeller's work capacity. When increasing the diameter of the inlet cover, the blade profile and placement angle should also be further adjusted to obtain the maximum impeller efficiency.
[0009] Preferably, the specific steps in step 3) are as follows: After optimization based on the Mach number of the impeller flow channel in step 2), the pressure ratio of the newly designed impeller will be significantly improved compared with the old design, while the efficiency will not decrease significantly compared with the later sections. Based on this, the relationship between the pressure ratio of each section and the total pressure ratio of the new design is as follows: Since the pressure ratio of the new design stage will be higher than that of the old design, under most conditions, M < N, that is, the number of stages of the new design is less than that of the old design. Further aiming at reducing the number of stages and based on the design requirements, the performance of the impeller of the new design can be rounded off. The rotational speeds of each stage and section can be adjusted according to the actual conditions, and the geometric parameters of the impeller can be further adjusted according to the space limitation.
[0010] Preferably, the method for determining the number of stages according to the principle of minimum work consumption is specifically as follows: S11. Determine the number of compressor stages and the pressure ratio of each stage according to the principle of minimum work consumption; S12. Check the stage division, pressure ratio distribution scheme and parameters determined according to the principle of minimum work consumption.
[0011] Preferably, the specific determination method in S11 is as follows: If the inlet temperature, polytropic efficiency and intercooler pressure loss ratio of each stage are the same, the work saving ratio can be calculated by Equation (1): 1) In the formula, N is the number of compressor stages; without subscript i is the overall machine parameter, and with subscript i is the corresponding parameter of stage i. is the pressure ratio of each stage, is the exponent coefficient of each stage, which can be calculated by Equation (2): 2) >In the formula, is the isentropic exponent of the gas; is the polytropic efficiency of each stage; By calculating the work saving ratio, the number of compressor stages can be determined according to the principle of minimum work consumption; The efficiency ratio of each stage is the same, that is, the ratio of the polytropic efficiency and the isentropic efficiency of each stage is the same. Then, in a multi-stage compressor, the total work consumption done by the rotor on the unit mass of gas is: 3) [[ID=This allows us to obtain the pressure ratio distribution for each stage based on the principle of compressor power saving.
[0012] Preferably, the verification method in S12 is as follows: 1) This method is based on computational fluid dynamics numerical simulation technology. It uses a computer to numerically solve the fluid dynamics control equations, abandoning the solution of the non-homogeneous Navier-Stokes equations analytically, and instead calculates the flow field parameters by solving the finite element numerical solution. 2) Based on the numerical simulation results, monitor the static temperature and static pressure at the impeller leading edge and trailing edge, the static temperature and static pressure at the diffuser inlet and outlet, and the static temperature and static pressure at the volute outlet, and calculate the adiabatic efficiency of each component using Equation 6). 6) In the formula, p is the static pressure, T is the static temperature, subscript 2 represents the tail edge and outlet of each component, and subscript 1 represents the leading edge and inlet; 3) Obtain the adiabatic efficiency of components such as the impeller, diffuser, and volute, respectively using... , , express; 4) Select diffuser efficiency as the verification parameter for the rationality analysis of determining the number of compressor stages based on the principle of minimum power saving, and set... When the diffuser efficiency is lower than this value, it can be considered that the principle of minimizing power consumption in determining the number of compressor stages is not reasonable enough, and a multi-stage compressor stage optimization method with impeller flow channel Mach number needs to be adopted.
[0013] The beneficial effects of this invention are as follows: Based on existing technology, this invention provides and supplements a method for optimizing and designing the number of stages of a multi-stage compressor after determining the number of stages according to the principle of minimum power saving. The method further optimizes and seeks the optimal design method for the number of stages of a multi-stage compressor by introducing the impeller inlet Mach number as the main reference parameter during the initial design process. Attached Figure Description
[0014] Figure 1 Diagram showing the blockage area where the medium is "clogging" the impeller; Figure 2 The diagram shows the relative Mach number of the medium on the meridional plane of each impeller section in the initial design; Figure 3 Mach number diagrams for the newly designed impeller channels of Section 2 and Section 3. Detailed Implementation
[0015] To enable those skilled in the art to more clearly understand the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments.
[0016] In the description of this invention, it should be understood that the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", "lateral", and "vertical" is based on the orientation or positional relationship shown in the accompanying drawings and is only for the convenience of describing this invention, and is not intended to indicate or imply that the device or component referred to must have a specific orientation, and therefore should not be construed as a limitation of this invention.
[0017] The invention will now be described in detail with reference to the accompanying drawings: Figure 1 As shown, a method for optimizing the number of stages in a multi-stage compressor based on the Mach number of the impeller channel is presented. After determining the number of stages based on the principle of minimum power saving, the method further optimizes and designs the number of stages of the multi-stage compressor based on the Mach number of the impeller channel. In the process of minimizing power saving, the impeller inlet Mach number is introduced as the main reference parameter, and a reliable method for optimizing and designing the number of stages of the multi-stage compressor is proposed. The method includes the following steps: 1) Calculate the Mach number of the impeller flow channel: The Mach number distribution in the meridional flow channel and the blade-to-blade flow channel can be obtained by using the Mach number calculation module in various CFD software. 2) Based on the Mach number of the impeller flow channel, increase the impeller speed, impeller outer diameter, and inlet cover diameter in the later section; 3) Apply impeller design based on the Mach number of the impeller flow channel with the goal of reducing the number of stages.
[0018] The specific method for increasing the impeller speed, impeller outer diameter, and inlet cover diameter in step 2) is as follows: 1) Increasing impeller speed: can significantly improve the impeller's work capacity. With the mass flow rate remaining constant, the impeller does more work on the gas medium, resulting in a greater increase in the gas pressure head and velocity head, ultimately leading to a higher pressure ratio; 2) Increase impeller outer diameter: Increasing the impeller outer diameter also means increasing the blade length, which in turn increases the work done by the impeller. When increasing the impeller outer diameter, the blade profile and placement angle should also be adjusted to obtain the maximum impeller efficiency. 3) Increase the diameter of the inlet cover: Increasing the diameter of the inlet cover will increase the inlet cross-sectional area, further reducing the loss of the medium at the impeller inlet. At the same time, it will increase the load at the turn of the impeller, slightly increasing the impeller's work capacity. When increasing the diameter of the inlet cover, the blade profile and placement angle should also be further adjusted to obtain the maximum impeller efficiency.
[0019] The specific steps in step 3) are as follows: After optimization based on the Mach number of the impeller flow channel in step 2), the pressure ratio of the newly designed impeller will be significantly improved compared with the old design, while the efficiency will not decrease significantly compared with the later sections. Based on this, the relationship between the pressure ratio of each section and the total pressure ratio of the new design is as follows: Since the pressure ratio of the new design stage is higher than that of the old design, under most conditions, M < N, that is, the number of stages of the new design is less than that of the old design. Further aiming at reducing the number of stages and based on the design requirements, the performance of the impeller of the new design can be rounded off. The rotational speeds of each stage and section can be adjusted according to actual conditions, and the geometric parameters of the impeller can be further adjusted according to space limitations.
[0020] The method for determining the number of stages according to the principle of minimum work consumption is specifically as follows: S11. Determine the number of compressor stages and the pressure ratio of each stage according to the principle of minimum work consumption; S12. Check the segmented, pressure ratio distribution scheme and parameters determined according to the principle of minimum work consumption.
[0021] Preferably, the specific determination method in S11 is as follows: If the inlet temperature, polytropic efficiency and intercooler pressure loss ratio of each stage are the same, the work-saving ratio can be calculated by Equation (1): (1) In the formula, N is the number of compressor stages; without subscript i is the parameter of the whole machine, and with subscript i is the corresponding parameter of stage i, is the pressure ratio of each stage, is the exponential coefficient of each stage, which can be calculated by Equation (2): (2) In the formula, is the isentropic exponent of the gas; is the polytropic efficiency of each stage; By calculating the work-saving ratio, the number of compressor stages can be determined according to the principle of minimum work consumption; The efficiency ratio of each stage is the same, that is, the ratio of the polytropic efficiency and the isentropic efficiency of each stage is the same. Then, in a multistage compressor, the total work consumption done by the rotor on the unit mass of gas is: (3) [[ID=4 (43)]] In the formula, R is the gas constant; is the inlet temperature of each stage. In the case of having an intercooler, except for the inlet temperature of the first stage, the others can be calculated according to the inlet water temperature and cooling efficiency of the intercooler. Preset the expected efficiency of each stage. When performing the thermal design of the pressure ratio distribution of each stage, only the pressure ratio of each stage is the unknown quantity. The partial derivative of the pressure ratio of each stage can be taken and the extreme value can be obtained. By联立各偏导式,可得: (4) Also: (53)]] (5) Thus, the pressure ratio distribution of each stage starting from the work saving of the compressor can be obtained.
[0022] It should be noted that there seems to be an error in the original text where "联立各偏导式,可得:" is in Chinese. It is translated as "By联立各偏导式,可得:" here, which may need to be corrected to a more accurate English expression according to the actual mathematical content. Also, the numbering in the translation is adjusted to match the correct sequence in the original text's meaning. For example, the original "4)" in ID 49 is translated and numbered as "(4)" in the translation of ID 49. And the "4)" in ID 50 should be "(5)" in the translation of ID 52 considering the context.Furthermore, because the volumetric flow rate decreases after gas compression, a smaller impeller outer diameter and a smaller outlet angle are required, resulting in a decrease in the impeller's work capacity. In this case, the pressure ratio of the later stages is typically reduced appropriately, while the pressure ratio of the earlier stages is appropriately increased. After several adjustments, the pressure ratio of each stage is determined.
[0023] S12. Verify the segmentation and pressure ratio allocation scheme determined by the principle of minimum power saving. However, the number of segments and pressure ratio determined based on the principle of minimum power saving are based on some assumptions, the main ones being: 1. The efficiency ratio of each segment is the same; 2. The expected efficiency of each segment is preset; 3. The derivation process only considers the efficiency of the impeller doing work on the gas, without considering the losses of other stationary components and the space and production costs brought about by more stages and intercoolers.
[0024] Therefore, it is necessary to verify the segmentation and pressure ratio allocation scheme determined by the principle of least power saving. If the prototype is produced according to the design scheme and the prototype fails to achieve the expected efficiency, it will result in a huge waste of resources.
[0025] The verification method in S12 is as follows: 1) This method is based on Computational Fluid Dynamics (CFD), a numerical simulation technique that uses computers to solve the governing equations of fluid dynamics. It abandons the analytical solution of the non-homogeneous Navier-Stokes equations, instead using finite element numerical solutions to calculate the flow field parameters. With the assistance of CFD technology, impeller, diffuser, and volute sections designed according to the principle of minimum power consumption can be efficiently constructed, and numerical simulations can be performed using the inlet and outlet pressures and temperatures specified in the design conditions. This method of using computers to numerically solve the governing equations of fluid dynamics abandons the analytical solution of the non-homogeneous Navier-Stokes equations, instead using finite element numerical solutions to calculate the flow field parameters. 2) Based on the numerical simulation results, monitor the static temperature and static pressure at the impeller leading edge and trailing edge, the static temperature and static pressure at the diffuser inlet and outlet, and the static temperature and static pressure at the volute outlet, and calculate the adiabatic efficiency of each component using Equation 6). 6) In the formula, p is the static pressure, T is the static temperature, subscript 2 represents the tail edge and outlet of each component, and subscript 1 represents the leading edge and inlet; 3) Obtain the adiabatic efficiency of components such as the impeller, diffuser, and volute, respectively using... , , This indicates that during the verification process, The efficiency is usually at a high level because the principle of minimizing power consumption primarily ensures the impeller's working efficiency. However, in actual manufacturing, the efficiency of the later stages may be lower than expected, severely impacting design effectiveness and operational efficiency. Numerical simulations of numerous multi-stage, multi-section compressors designed based on the principle of minimum power saving revealed the following reasons for this phenomenon: 1. In the later stages of the compressor, diffuser, and volute, the pressure and density of the gas medium are significantly increased, resulting in a decrease in volumetric flow rate. Consequently, the outer diameter and outlet angle of the impeller in the later stages are smaller. 2. Therefore, the work capacity of the impeller in the later stages is smaller, limiting the rise in both the pressure head and velocity head of the gas. 3. To achieve sufficient pressure boost and convert more of the gas velocity head into pressure head, the outer diameter of the diffuser needs to be further enlarged. 4. Ultimately, this leads to an increase in the entropy of the gas within the diffuser and a significant increase in energy loss due to viscous friction, while the pressure head and pressure ratio remain at a low level. 5. Due to the large number of stages and sections, the gas medium inevitably experiences significant frictional losses or secondary flow losses in each flow path.
[0026] 4) Select diffuser efficiency as the verification parameter for the rationality analysis of determining the number of compressor stages based on the principle of minimum power saving, and set... When the diffuser efficiency is lower than this value, it can be considered that the principle of minimizing power consumption in determining the number of compressor stages is not reasonable enough, and a multi-stage compressor stage optimization method with impeller flow channel Mach number needs to be adopted.
[0027] Mach number is a dimensionless number representing the ratio of fluid velocity to the local speed of sound in the same fluid. Since the local speed of sound in a fluid is related to the physical properties of the fluid medium (mainly density), the physical properties of the medium change constantly within a compressor, and therefore the speed of sound also changes constantly. Therefore, calculating the Mach number in a flow channel requires simultaneously calculating the fluid velocity and the local speed of sound within the impeller flow channel. Manually calculating the Mach number within the impeller flow channel is tedious and complex; however, many CFD software programs include Mach number calculation modules, which can quickly obtain the Mach number distribution in meridional and blade-to-blade flow channels.
[0028] When the fluid velocity in a certain region of the impeller flow channel exceeds the local Mach number, blockage occurs. When blockage occurs, because the velocity of the pressure wave (as a mechanical wave) is the local speed of sound, the velocity and pressure of the fluid medium cannot increase further before blockage. The medium becomes "blocked" in the blockage area of the impeller, such as... Figure 1 As shown, the upstream gas velocity exceeds the local Mach number, causing congestion and resulting in large cavitation downstream, inducing secondary flow. Congestion significantly reduces impeller efficiency, a phenomenon that must be avoided in impeller design.
[0029] For impellers designed based on the principle of minimum power saving, the local Mach number of the internal medium is generally low. This is because, on the one hand, the pressure and density of the gas medium in the later section increase, and the relative sound velocity increases; on the other hand, the outer diameter and outlet angle of the impeller are small, which also limits the velocity of the gas medium inside the impeller.
[0030] S22. Based on the Mach number of the impeller flow channel, increase the impeller speed, impeller outer diameter, and inlet cover diameter of the downstream section.
[0031] For impellers designed based on the principle of minimum power saving, if the Mach number amplitude of the flow channel is low, such as around 0.5-0.6, it indicates that the rotational speed, impeller outer diameter, and inlet cover diameter can be further increased. Increasing the impeller speed significantly improves its work capacity. With a constant mass flow rate, the impeller performs more work on the gas medium, leading to a greater increase in the gas pressure head and velocity head, ultimately translating into a higher pressure ratio. However, the increased speed slightly reduces the control effect of the blade boundary layer on the secondary flow, resulting in a slight decrease in impeller efficiency. Comparing impellers designed based on the principle of minimum power saving, the overall efficiencies of the two designs are usually not significantly different due to the greater efficiency losses within the diffuser. Furthermore, changes in impeller speed necessitate further adjustments to the number of blades, blade profile, and placement angle to maintain optimal flow conditions within the impeller and minimize efficiency losses.
[0032] Increasing the impeller's outer diameter is another way to improve its work capacity. A larger outer diameter means a longer blade length, which in turn increases the impeller's work output. When increasing the impeller's outer diameter, the blade profile and placement angle should also be further adjusted to achieve maximum impeller efficiency.
[0033] Increasing the inlet shroud diameter increases the inlet cross-sectional area, further reducing media loss at the impeller inlet. It also increases the load at the impeller bend, slightly improving the impeller's work capacity. When increasing the inlet shroud diameter, the blade profile and placement angle should also be adjusted to achieve maximum impeller efficiency.
[0034] The above parameters can be adjusted in combination, and impeller parameterization optimization methods can be used simultaneously. During the adjustment process, the Mach number of the impeller flow channel must always be kept below the threshold. Generally, in flows with Mach numbers less than 0.85, the magnitude of separation loss is low; therefore, the Mach number in most areas of the impeller flow channel should be kept below 0.85, and the Mach number in all areas should not exceed 0.9.
[0035] S23. Apply impeller design based on the Mach number of the impeller flow channel with the goal of reducing the number of stages.
[0036] After optimization based on the impeller passage Mach number in S22, the pressure ratio of the newly designed impeller will be significantly higher than that of the old design, and at the same time, the efficiency will not decrease significantly compared to the subsequent stages. On this basis, the relationship between the pressure ratios of each stage and the total pressure ratio of the new design is shown in Equation (7): Since the pressure ratio of the newly designed stage will be higher than that of the old design, under most conditions, M < N, that is, the number of stages of the new design is less than that of the old design. At this time, further aiming at reducing the number of stages and based on the design requirements, continue to round the performance of the newly designed impeller. The rotational speeds of each stage and section can be adjusted according to actual conditions, and the geometric parameters of the impeller can be further adjusted according to space limitations.
[0037] The advantages of applying the impeller design based on the impeller passage Mach number with the goal of reducing the number of stages are as follows: First, in terms of cost, the manufacturing and assembly of the impeller, diffuser, volute, and other accessory components in one stage are eliminated. At the same time, in the overall structure of the machine, the number of applications of the intercooler, the complexity of the structure, and the space occupation can be reduced. At the performance level, since the number of stages and sections that the gas medium needs to pass through is reduced, the losses of the pipelines and components between stages, the losses of the intercooler, as well as its mechanical losses and leakage losses can be avoided. At the same time, the efficiency of the newly designed impeller will not decrease significantly, which will be reflected as an increase in efficiency at the overall machine level.
[0038] Therefore, after optimizing and designing the number of stages of a multistage compressor based on the impeller passage Mach number, if the number of stages can be reduced compared to the design based on the traditional minimum work principle, and the efficiency of the new design is not significantly reduced (which can be achieved through the optimized design of the impeller and verified by numerical simulation), the production and manufacturing cost of the overall machine can be effectively controlled, and the performance of the overall machine can be improved. Embodiment
[0039] The following will more clearly and completely illustrate the present invention by way of an embodiment in conjunction with the drawings, but the present invention is not limited to the scope of the described embodiment. In this embodiment, a certain type of multistage centrifugal compressor is taken as the optimization object, and the number of stages design and pressure ratio distribution of this compressor are designed according to the minimum work principle. During the application process, it is found that the efficiency of this compressor is not ideal. Therefore, the method described in the present invention is used to further explore the unreasonable points of the original design and the optimization method.
[0040] 1. Rationality analysis of determining the number of stages of the compressor based on the minimum work principle: This type of multistage centrifugal compressor designed according to the minimum work principle has a total of 4 stages, with only 1 stage in each stage. The pressure ratio distribution of each stage is shown in Table 1: Table 1 Section 1 Section 2 Section 3 Section 4 Total pressure ratio pressure ratio 1.93 1.81 1.61 1.43 6.37 The overall pressure ratio is slightly less than the product of the pressure ratios of the four stages because there are varying degrees of pressure loss in each stage, inter-stage piping, intercooler, and other components of the entire unit. The pressure ratio decreases progressively from stage 1 to stage 4 because the impeller outer diameter and outlet angle are reduced due to the increased medium pressure in the later stages in the design based on the principle of minimizing power consumption. The impeller of this multi-stage centrifugal compressor adopts a modular impeller design from advanced foreign models, the diffuser is a bladeless diffuser, and the volute is a circular cross-section asymmetrical inner volute.
[0041] After manufacturing and assembly, the overall efficiency of this model was not ideal, and the adiabatic efficiency of the later stages was lower during measurement. In order to investigate the reasons for the low efficiency of the original design and to further optimize the model, the rationality analysis method for determining the number of compressor stages based on the minimum power saving principle described in this invention was used for analysis.
[0042] The CFD method was used to model and numerically simulate the impeller, diffuser, and volute of each section, and the efficiency of each component in each section is shown in Table 2. Table 2 efficiency Section 1 Section 2 Section 3 Section 4 Up to the impeller 95.03% 95.39% 96.64% 96.20% Cut-off diffuser 90.73% 90.67% 87.74% 84.24% Up to the snail shell 87.79% 88.52% 85.63% 82.29% The pressure ratios of each impeller and diffuser section are shown in Table 3: Table 3 pressure ratio Section 1 Section 2 Section 3 Section 4 impeller 1.58 1.55 1.43 1.30 Impeller + Diffuser 1.95 1.81 1.63 1.43 CFD analysis reveals that although the excellent impeller design maintains high efficiency, the smaller outer diameter and outlet angle of the later stages result in relatively lower work capacity. To maintain the pressure ratio in these later stages, the diffuser's outer diameter and meridional channel length must be increased accordingly, leading to a significant decrease in diffuser efficiency. The additional losses caused by the diffuser relative to the impeller in stages 1 to 4 are 4.30%, 4.72%, 8.90%, and 11.96%, respectively. The efficiency losses in the later stages, namely stages 3 and 4, are substantial. If an 8% efficiency benchmark is used, stages 3 and 4 of this type of multi-stage centrifugal compressor, designed based on the principle of minimum power saving, are not sufficiently optimized.
[0043] Furthermore, by adjusting the outer diameter of the bladeless diffuser downwards, i.e. by reducing the length of the diffuser meridional flow channel, the diffuser efficiency loss can be reduced. However, this comes at the cost of further reducing the pressure ratio of this section, which may cause the compressor performance to fail to meet the design requirements. Therefore, it is necessary to further optimize the design by adopting the multi-stage compressor stage number optimization method based on the impeller flow channel Mach number described in this invention.
[0044] 2. Based on the Mach number of the impeller flow channel, increase the impeller speed, impeller outer diameter, and inlet cover diameter of the downstream section.
[0045] First, the Mach number of the impeller channel is checked, and its amplitude is examined. If the value is close to 1, it is impossible to further optimize the number of compressor stages based on the impeller channel Mach number. If the value is still close to 1 and has room for improvement, further optimization is possible. This process is implemented using the CFD software AXCENT. In the initial design, the relative Mach number of the medium in the meridional plane of each impeller section is as follows: Figure 2 As shown; After calculation and verification, except for the impeller shroud side channel of section 1 which always maintains a high Mach number, the impeller flow channel Mach numbers of the other three sections are far from reaching the critical value, and the speed of the impeller, the outer diameter of the impeller, and the diameter of the inlet shroud can be further increased in the later sections.
[0046] 3. With the goal of reducing the number of stages, apply impeller design based on the Mach number of the impeller flow channel, and re-plan the number of stages and the pressure ratio of each stage.
[0047] By checking the Mach number of the impeller flow channel, it can be found that there is room to increase the impeller speed, impeller outer diameter, and inlet cover diameter in sections 2 to 4. Therefore, the goal is to reduce the number of sections in this multi-stage centrifugal compressor, that is, from 4 sections to 3 sections (while maintaining the corresponding pressure ratio), in order to reduce manufacturing costs and space occupation.
[0048] Further adjust the speed. In the original design, all impeller sections were coaxial and rotated at the same speed. The new design uses large and small gears to position sections 1, 2, and 3 on different shafts. Section 1 maintains its original speed, while sections 2 and 3 have their speeds increased to the same value. Keeping the impeller flow channel Mach number below the threshold, the speeds of sections 2 and 3 are increased from 5330 to 6880 after calculation. Further adjust the outer diameter of the impeller in section 2 and the inlet cover diameter based on the new design speed, and optimize the blade profile to achieve high efficiency. This optimization process can employ neural network algorithms, annealing algorithms, or other optimization methods, or find suitable replacement impellers or modular impellers in the design library. During the optimization design process, the principles of ensuring the Mach number in the new impeller flow channel does not exceed the critical value and that the Mach numbers of each impeller flow channel are similar should be followed, and the product of the pressure ratios of each section of the new impeller should equal the overall machine design pressure ratio.
[0049] The Mach number of the newly designed section 2 and section 3 impeller flow channels is as follows: Figure 3 As shown, in the new design, the Mach number of the impeller channels in sections 1-3 is increased according to the design method, and the Mach number in most areas does not exceed 0.85, with the maximum value not exceeding 0.9.
[0050] Furthermore, the efficiency of each section in the original design and the new design are compared, as shown in Table 4, and the pressure ratio of each section is shown in Table 5.
[0051] Table 4 efficiency Old design New design Section 1 87.79% 87.79% Section 2 88.52% 86.68% Section 3 85.63% 83.99% Section 4 82.29% Table 5 pressure ratio Old design New design Section 1 1.95 1.95 Section 2 1.81 2.02 Section 3 1.63 1.74 Section 4 1.43 Total pressure ratio 6.37 6.37 A multi-stage compressor stage optimization design based on impeller inlet Mach number was adopted. Compared to the original design based on the principle of minimum power saving, the efficiency of stage 2 and stage 3 decreased by 1.84% and 1.64% respectively. However, due to the redesign of the speed and impeller, the total number of stages can be directly reduced from 4 to 3. From a production cost perspective, the design, production, and assembly of one stage's impeller, diffuser, volute, casing, piping, and intercooler can be eliminated, significantly reducing production costs. From a space and structural layout perspective, it can effectively save space and make the structural layout more flexible. In terms of performance, although the efficiency of the two stages decreased slightly, the effect of reducing the number of stages is to avoid leakage losses, mechanical losses, and friction losses in the first stage, resulting in an overall efficiency improvement. On the other hand, compared to the old design, the pressure ratio of stage 2 and stage 3 is also increased, and the inter-stage losses are reduced. Although the number of stages is reduced, the overall pressure ratio does not decrease. Finally, the power consumption of each segment in the original design and the optimized design was verified. The four segments in the original design were 2305kW, 2139kW, 1741kW and 1312kW, with a total power consumption of 7497kW. The three segments in the optimized design were 2305kW, 2769kW and 1851kW, with a total power consumption of 6925kW, thus achieving a reduction in power consumption.
[0052] The above embodiments clearly demonstrate the advantages of impeller design based on the Mach number of the impeller channel. By redesigning and reproducing the number of stages and the impeller, the number of design stages is reduced, production costs are saved, and the structural layout is improved, thereby achieving design optimization of multi-stage compressors while ensuring that the design performance remains unchanged or is slightly improved.
[0053] The specific embodiments described herein are merely illustrative of the principles and effects of the invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this invention should still be covered by the claims of this invention.
Claims
1. A method for optimization of number of stages in a multistage compressor based on blade row passage Mach number, characterized by, The method further comprises a multi-stage compressor stage number optimization and design method based on impeller flow channel Mach number after determining the stage number according to the least work principle. In the process of the least work principle, a reliable method for optimization and design of the multi-stage compressor stage number optimization and design method is proposed by introducing the impeller inlet Mach number as the main reference parameter. The method comprises the following steps: 1) calculating the impeller flow channel Mach number: the Mach number distribution in the meridional plane flow channel and the blade-to-blade flow channel can be obtained through the Mach number calculation module in various CFD software; 2) increasing the impeller speed, impeller outer diameter and inlet shroud diameter of the rear stage according to the impeller flow channel Mach number; 3) applying the impeller design based on the impeller flow channel Mach number to reduce the stage number.
2. The method for multi-stage compressor segment number optimization based on impeller passage Mach number of claim 1, wherein, The specific method for increasing the impeller speed, impeller outer diameter and inlet shroud diameter in step 2) is as follows: 1) increasing the impeller speed: the impeller work capacity can be significantly improved, and under the condition of constant mass flow, the impeller does more work on the gas medium, so that the pressure head and velocity head of the gas are increased, and finally converted into higher pressure ratio; 2) increasing the impeller outer diameter: the increase of the impeller outer diameter represents the increase of the blade length, and the work capacity of the impeller is increased accordingly; when the impeller outer diameter is increased, the blade profile and setting angle should also be adjusted to obtain the maximum impeller efficiency; 3) increasing the inlet shroud diameter: increasing the inlet shroud diameter will increase the inlet cross-sectional area, further reducing the loss of the medium at the impeller inlet, and increasing the load at the turning part of the wheel disc, slightly increasing the work capacity of the impeller; When the inlet shroud diameter is increased, the blade profile and setting angle should also be further adjusted to obtain the maximum impeller efficiency.
3. The method for multi-stage compressor segment number optimization based on impeller passage Mach number of claim 1, wherein, The specific steps in step 3) are as follows: after optimization based on the impeller flow channel Mach number in step 2), the pressure ratio of the newly designed impeller will be significantly higher than that of the old design, and the efficiency of the rear stage will not decrease significantly. On this basis, the relationship between the pressure ratio of each stage and the total pressure ratio of the newly designed impeller is as follows: Since the pressure ratio of the newly designed stage will be higher than that of the old design, under most conditions, M < N, i.e. the stage number of the newly designed impeller is less than that of the old design. Further, in order to reduce the stage number, the performance of the newly designed impeller is continuously rounded according to the design requirements. The rotational speed of each stage can be adjusted according to the actual conditions, and the geometric parameters of the impeller can be further adjusted according to the space limitation.
4. The method for multi-stage compressor segment number optimization based on impeller passage Mach number of claim 1, wherein, The method for determining the stage number according to the least work principle comprises the following steps: S11, determining the stage number of the compressor and the pressure ratio of each stage according to the least work principle; S12, checking the segmentation, pressure ratio distribution scheme and parameters determined according to the least work principle.
5. The method for multi-stage compressor segment number optimization based on impeller passage Mach number of claim 4, wherein The specific determination method in S11 is as follows: The brake specific fuel consumption (BSFC) is calculated by equation 1) as follows: The brake specific fuel consumption (BSFC) is calculated by equation 1) as follows: 1） where N is the number of compressor stages; the parameters without subscript i are for the entire machine, and the parameters with subscript i are for stage i, is the pressure ratio for each stage, is the exponent coefficient for each stage, which can be calculated by equation 2): 2） wherein is the gas isentropic exponent; is the polytropic efficiency of each stage; By calculating the work-saving ratio, the stage number of the compressor can be determined according to the least work principle; Efficiency ratio of stages The same, i.e. the ratio of the polytropic and isentropic efficiencies of each stage, then in a multi-stage compressor the total work done by the rotor on the unit mass of gas is: 3） where R is the gas constant; The inlet temperature of each section is calculated, and in the case of having a intercooler, the inlet temperature of the rest of the sections can be calculated according to the inlet water temperature and cooling efficiency of the intercooler. When the expected efficiency of each section is preset, and the thermodynamic design of the pressure ratio distribution of each section is performed, only the pressure ratio of each section is an unknown quantity. The partial derivative of each section pressure ratio can be solved and the extreme value can be obtained. By solving the simultaneous partial derivative equations, the following equation can be obtained: 4） Therefore, the pressure ratio distribution of each stage starting from the work-saving of the compressor can be obtained. 5） The checking method in S12 is as follows:
6. The method for multi-stage compressor segment number optimization based on impeller passage Mach number of claim 4, wherein, 1) This method is based on the numerical simulation technology of computational fluid dynamics, which uses a computer to solve the control equations of fluid mechanics. Instead of solving the analytical solution of the non-homogeneous N-S equation, the method of solving the finite element numerical solution is used to calculate the flow field parameters. 2) According to the numerical simulation results, the static temperature and static pressure of the leading edge and the trailing edge of the impeller, the static temperature and static pressure of the inlet and outlet of the diffuser, and the static temperature and static pressure of the outlet of the volute are monitored, and the adiabatic efficiency of each component is calculated through equation 6); 6） In the formula, p is the static pressure, T is the static temperature, subscript 2 represents the trailing edge and the outlet of each component, and subscript 1 represents the leading edge and the inlet; 3) the adiabatic efficiency of the impeller, diffuser, volute, etc. parts are represented by , , respectively; 4) Select the diffuser efficiency as the check parameter of the reasonability analysis of the number of compressor stages determined by the minimum work principle, set When the diffuser efficiency is lower than the value, it can be considered that the number of compressor stages determined by the minimum work principle is not reasonable enough, and the multi-stage compressor stage number optimization method of impeller flow passage Mach number needs to be used.